1. Field of the Invention
The present invention is directed to an auto-tensioner which provides an adequate tension to an engine timing-belt for reducing noise therefrom and improving life thereof and, more particularly, to a so-called free piston type auto-tensioner having a body in which a piston is moved.
2. Description of the Prior Art
Japanese Utility Model Laid-open Print No. Hei.5-38422, published on May 25, 1993, without examination, discloses a conventional auto-tensioner. This auto-tensioner has a rod which extends from a body and is in engagement with an engine timing belt. In the body, the rod is configured to an enlarged portion which is slidably mounted on a sleeve fixed to the body. A pressure chamber which is filled with an amount of fluid is defied between the sleeve and the rod. To establish the foregoing engagement of the rod with the engine timing belt, the auto-tensioner is installed in an engine compartment of a vehicle body in such a manner that the rod is brought into upstanding or upright condition.
Under the resultant arrangement, in the event of the unexpected existence of one or more air bubbles in the pressure chamber, the upward movement of each air bubble is prevented by collision thereof with the rod. This means that the air bubbles remain in the pressure chamber, thereby disturbing the damping function of the rod; that is to say, the designed operation of the auto-tensioner fails to function.
Accordingly, a need exists for an auto-tensioner without the foregoing drawback.
The present invention has been developed to satisfy the need noted above and thus has as a primary object the provision of a free piston type auto-tensioner for providing a continual adequate tension to a belt-shaped power transmission member which comprises:
a cylindrical body;
a rod fitted in the body so as to be moved back and forth along its axial direction, extending outside the body so as to urge the belt-shaped power transmission member via an idler pulley;
a block placed in the body and having one end portion and the other end portion, one end portion of the block receiving the rod movably and defining therein a first fluid chamber together with the rod for storing a fluid, the other end portion defining a second fluid chamber together with a movable piston, the block being provided with a fluid passage connected between the first fluid chamber and the second fluid chamber;
a first urging member formed into a hollow configuration and urging the rod to extend the same outside the body;
a second urging member formed into a cylindrical configuration and urging the piston for increasing pressure in the second fluid chamber;
damping means controlling a fluid communication between the first fluid chamber and the second chamber for adjusting an engagement of the idler pulley with the belt-shaped power transmission member in such a manner that when a tension thereof is decreased, a quick propulsive movement of the idler pulley to the belt-shaped power transmission member is allowed by the first urging member, while when the tension is increased, the idler pulley is retracted gradually from the belt-shaped power transmission member by a registration of the belt-shaped power transmission member.